Process for producing multilayer printed wiring board

ABSTRACT

Multi-layer printed wiring boards may be produced by:
     (1) conveying an adhesive sheet from an adhesive sheet roll wherein an adhesive sheet having a prepreg formed on a support film is wound in a roll and placing the adhesive sheet such that a prepreg surface contacts one or both of the surfaces of a circuit board,   (2) partially adhering the adhesive sheet to the circuit board by heating and pressing a part of the adhesive sheet from the support film side, and cutting the adhesive sheet according to the size of the circuit board with a cutter,   (3) heating and pressing the temporarily fitted adhesive sheet under reduced pressure to laminate the adhesive sheet on the circuit board,   (4) forming an insulating layer by thermally curing the prepreg, and   (5) detaching the support film after the thermal curing step.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationNo. PCT/JP2008/066374, filed on Sep. 11, 2008, and claims priority toJapanese Patent Application No. 2007-235621, filed on Sep. 11, 2007, andJapanese Patent Application No. 2007-239671, filed on Sep. 14, 2007, allof which are incorporated herein by reference in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods for producing a multi-layerprinted wiring board, and particularly, methods of producing amulti-layer printed wiring board by a buildup method using a prepreg.

2. Discussion of the Background

Conventionally, when a prepreg is used for forming an insulating layerof a multi-layer printed wiring board, it is a general practice to layera prepreg on an inner layer circuit board, and pressurize and heat witha hot press or a vacuum laminating machine one by one. For example,JP-A-2003-332740 discloses a method of forming an insulating layer on acircuit board one by one by treating a glass cloth prepreg and a copperfoil with a vacuum pressing-type laminating machine. However, in view ofthe recent preference toward downsized and thinner electronic devices,there is an increasing demand for ultrafine wiring also in a printedwiring board having a multi-layer structure. To meet the need, it isadvantageous to form a conductive layer by plating according to asemi-additive method rather than forming a conductive layer with acopper foil. In addition, formation of an insulating layer one by onecannot be said to be a satisfactory method also from the productivity.JP-A-2003-340952 discloses a method of producing a multi-layer printedwiring board using a stage B resin composition sheet with a releasefilm, which is obtained by adhering by lamination of a sheet, wherein astage B resin composition for additive is adhered to one surface of arelease film, on a fiber cloth substrate. While this method enablesformation of a conductive layer by plating, a vacuum press apparatus isused for forming an insulating layer and an insulating layer is alsoformed one by one. Thus, it cannot be said to be a satisfactory methodfrom the productivity. A production method of an insulating layer of amulti-layer printed wiring board using a prepreg, which enablesformation of a conductive layer by a semi-additive method withoutforming the layer one by one has not been put to practical use.

SUMMARY OF THE INVENTION

Accordingly, it is one object of the present invention to provide amethod of producing a multi-layer printed wiring board that enablescontinuous production of an insulating layer of a multi-layer printedwiring board with a prepreg and without forming one by one.

As a production technique of a multi-layer printed wiring board, aproduction method based on a buildup method, which includes alternatelysuperimposing an insulating layer and a conductive layer, is known.Moreover, as a method of forming an insulating layer of a multi-layerprinted wiring board, a method including continuously forming aninsulating layer from an adhesive film, which has a thermosetting resinlayer formed on a support film, using an autocutter and a vacuumlaminating machine is known. Since the method uses an adhesive filmrather than a prepreg, continuous production is possible without formingone by one. Generally, according to this method, first in an autocutter, an adhesive film wound in a roll is conveyed onto a circuitboard and, after partial thermal compression bonding of the adhesivefilm, cut according to the size of a circuit board, and the adhesivefilm is temporary fitted to the circuit board. Thereafter, the adhesivefilm is laminated on the circuit board by a vacuum laminating machine, asupport film is detached, and an insulating layer is formed by thermalcuring. After forming the insulating layer, a conductive layer can beformed by plating according to a semi-additive method.

As mentioned above, however, a production technique of a multi-layerprinted wiring board also varies for a prepreg having mechanicalproperties and the like, which are greatly different from those of anadhesive film, and formation of an insulating layer one by one isgenerally employed. As pointed out in JP-A-2003-332740, moreover,prepregs were generally assumed for use in methods wherein a prepreg issandwiched between mirror panels and adhered by heating and pressuringto form a multilayer. Therefore, when conventional prepregs are appliedto a vacuum laminating machine, flowability sufficient to cover circuitconcaves and convexes on an inner layer circuit board cannot beafforded. On the other hand, when flowability of a resin compositionused for impregnating a prepreg is secured so that the circuit concavesand convexes can be sufficiently covered, the flowability of the resinbecomes too high during a thermal curing step after vacuum lamination,which causes exuding of resin, exposure of fiber substances such asglass cloth and the like on the surface of an insulating layer, and thelike, thus interfering with the formation of the insulating layer.Accordingly, it is difficult to apply a prepreg to the above-mentionedmethod wherein a laminating step is separated from a curing step. Forexample, JP-A-2005-154727 discloses a thermosetting resin compositionhaving a molten viscosity suitable for formation of an insulating layerof a multi-layer printed wiring board by a vacuum laminating machine anda prepreg to be impregnated therewith. The prepreg is described to bealso produceable by, in the same manner as with an adhesive film,laminating on a circuit board by a vacuum laminating method and curingby heating. In the Examples, eventually, a multi-layer printed wiringboard was produced one by one only by a method including vacuumlamination press via a release film.

In view of such situation, the present inventors have made intensivestudies and found that, when an insulating layer is formed by laminatingan adhesive sheet, wherein a prepreg is formed on a support film, on acircuit board, and thermal curing the prepreg without detaching thesupport film, an insulating layer can be formed without exuding of aresin from the prepreg in a thermal curing step even when the prepregcomprises a thermosetting resin composition having flowabilitysufficient to cover circuit concaves and convexes.

On the other hand, when the prepreg is thermally cured without detachingthe support film, the support film cannot be detached easily aftercuring. Thus, it is necessary to use a support film with a release layerto enable detachment of the prepreg (insulating layer) after curing fromthe support film via the release layer. When a release layer isprovided, a phenomenon was found during the study of the presentinventors in which a support film was detached from a prepreg in an autocutter in the process of conveying the adhesive sheet, thus makingcontinuous production difficult to perform. Thus, the present inventorshave further conducted intensive studies and found that, in a supportfilm with a release layer, which enables detachment of the support filmeven after curing from the cured prepreg, stable continuous productionis possible by setting the peel strength of the support film from theprepreg before thermal curing to not less than a predetermined level.

The present inventors have completed the present invention based on thefindings as mentioned above. Therefore, the present invention providesthe following.

(1) A method of producing a multi-layer printed wiring board comprising:

(a) a temporary fitting preparatory step comprising conveying anadhesive sheet from an adhesive sheet roll wherein an adhesive sheethaving a prepreg formed on a support film is wound in a roll and placingthe adhesive sheet such that a prepreg surface contacts one or both ofthe surfaces of a circuit board;

(b) a temporary fitting step for temporarily fitting the adhesive sheetto the circuit board, comprising partially adhering the adhesive sheetto the circuit board by heating and pressing a part of the adhesivesheet from the support film side, and cutting the adhesive sheetaccording to the size of the circuit board with a cutter;

(c) a laminating step comprising heating and pressing the temporarilyfitted adhesive sheet under reduced pressure to laminate the adhesivesheet on the circuit board;

(d) a thermal curing step comprising forming an insulating layer bythermally curing the prepreg; and

(e) a detaching step comprising detaching the support film after thethermal curing step.

(2) The method of the above-mentioned (1), wherein, in the adhesivesheet, the support film has a release layer on the surface side incontact with the prepreg, and the peel strength of the support film fromthe prepreg before thermal curing is not less than 1.5 gf/50 mm at180-degree peel strength.

(3) The method of the above-mentioned (1) or (2), wherein, in theadhesive sheet, the support film has a thickness of 20 to 50 μm and theprepreg has a thickness of 20 to 100 μm.

(4) The method of any of the above-mentioned (1) to (3), wherein thetemporary fitting preparatory step and the temporary fitting step areperformed by an auto cutter.

(5) The method of any of the above-mentioned (1) to (4), wherein thelaminating step is performed by a vacuum laminating machine.

(6) The method of any of the above-mentioned (1) to (5), wherein theadhesive sheet has a layer constitution of protectionfilm/prepreg/support film, and the protection film is detached bywinding during conveying of the adhesive sheet in the temporary fittingpreparatory step.

(7) The method of the above-mentioned (6), wherein, in the adhesivesheet, the protection film has a thickness of 5 to 30 μm.

(8) The method of any of the above-mentioned (1) to (7), wherein theheating and pressing are performed via an elastic material in thelaminating step.

(9) The method of the above-mentioned (8), further comprising, after thelaminating step, a smoothing step of heating and pressing the adhesivesheet under normal pressure with a metal plate.

(10) The method of any of the above-mentioned (1) to (9), furthercomprising a drilling step for drilling the insulating layer, aroughening step for roughening the insulating layer, a plating step forforming a conductive layer on the roughened insulating layer surface byplating, and a circuit forming step for forming a circuit on aconductive layer.

(11) The method of any of the above-mentioned (1) to (10), wherein thedrilling step is performed between the thermal curing step and thedetaching step.

(12) The method of the above-mentioned (10) or (11), wherein thedrilling step comprises forming a via hole by applying a carbon dioxidegas laser on the top of the support film.

(13) The method of the above-mentioned (12), wherein the carbon dioxidegas laser has an energy of not less than 1 mJ.

(14) The method of the above-mentioned (12), wherein the energy of thecarbon dioxide gas laser is 1 mJ to 5 mJ.

(15) The method of any of the above-mentioned (1) to (14), wherein thesupport film is a poly(ethylene terephthalate) film.

(16) The method of any of the above-mentioned (1) to (15), wherein theprepreg comprises a glass cloth impregnated with a thermosetting resincomposition.

The production method of the present invention can continuously producean insulating layer of a multi-layer printed wiring board with a prepregwithout forming one by one. In other words, even when an insulatinglayer is formed by lamination of an adhesive sheet by a vacuumlaminating machine and thermal curing, inconveniences such as exposureof prepreg fiber due to exuding of resin and the like do not occur, andan insulating layer superior in covering circuit concaves and convexescan be formed. In addition, an adhesive sheet wherein a prepreg isformed on a support film can be used as being wound in a roll in an autocutter and the like, and can be temporarily fit to a circuit boardcontinuously without detachment of the support film from the prepregduring conveying. Furthermore, by combining with a step of forming aconductive layer by plating according to a semi-additive method and thelike, a built-up format using a prepreg becomes available, and aproduction method of a printed wiring board having high productivity canbe provided.

Since an insulating layer formed from a prepreg is superior in themechanical strength, the present invention is particularly useful forthe production of a thin multi-layer printed wiring board such as a thincore substrate, a coreless substrate omitting a core substrate, and thelike.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same become betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a figure containing scanning electron microscope (SEM)photographs showing the results of Examples 4 to 6.

FIG. 2 is a figure containing scanning electron microscope (SEM)photographs showing the results of Comparative Examples 3 to 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is explained in the following by referring to apreferable embodiment thereof.

The prepreg of the present invention can be obtained by impregnating asheet fiber substrate with a thermosetting resin composition, followedby heating and drying.

As the sheet fiber substrate, those conventionally used as a substratefor prepreg such as glass cloth, aramid non-woven fabric, liquid crystalpolymer non-woven fabric and the like can be used. Glass cloth isparticularly preferable. In addition, when used for forming aninsulating layer of a multi-layer printed wiring board, a thin-typesubstrate having a thickness of not more than 50 μm is preferably used.

As specific examples of the sheet fiber substrate, a glass clothsubstrate includes STYLE1027MS (warp yarn density 75 yarns/25 mm, weftyarn density 75 yarns/25 mm, cloth weight 20 g/m², thickness 19 μm) and1037MS (warp yarn density 70 yarns/25 mm, weft yarn density 73 yarns/25mm, cloth weight 24 g/m², thickness 28 μm) manufactured byAsahi-Schwebel Co., Ltd., and 1037NS (warp yarn density 72 yarns/25 mm,weft yarn density 69 yarns/25 mm, cloth weight 23 g/m², thickness 21μm), 1027NS (warp yarn density 75 yarns/25 mm, weft yarn density 75yarns/25 mm, cloth weight 19.5 g/m², thickness 16 μm), and 1015NS (warpyarn density 95 yarns/25 mm, weft yarn density 95 yarns/25 mm, clothweight 17.5 g/m², thickness 15 μm) manufactured by Arisawa Mfg. Co.,Ltd. and the like.

Examples of the liquid crystal polymer non-woven fabric include VECLS(fabric weight 6 to 15 g/m²), Vectran and the like made from an aromaticpolyester non-woven fabric by a melt-blow method (manufactured byKuraray Co., Ltd.).

As the thermosetting resin composition, any can be used without anyparticular limitation as long as it is suitable for the insulating layerof a multilayer printed wiring board. For example, a compositioncontaining at least a thermosetting resin such as epoxy resin, cyanateester resin, phenol resin, bismaleimide-triazine resin, polyimide resin,acrylic resin, vinylbenzyl resin, and the like and a curing agentthereof can be used. Preferred is a composition containing an epoxyresin as a thermosetting resin, for example, a composition containing anepoxy resin, a thermoplastic resin, and a curing agent.

Examples of the epoxy resin include a bisphenol A type epoxy resin,biphenyl type epoxy resin, naphthol type epoxy resin, naphthalene typeepoxy resin, bisphenol F type epoxy resin, phosphorus containing epoxyresin, bisphenol S type epoxy resin, alicyclic epoxy resin, aliphaticchain epoxy resin, phenol novolac type epoxy resin, cresol novolac typeepoxy resin, bisphenol A novolac type epoxy resin, epoxy resin havingbutadiene structure, diglycidyl etherified product of bisphenol,diglycidyl etherified product of naphthalenediol, glycidyl etherifiedproduct of phenols, and diglycidyl etherified product of alcohols, andan alkyl substituted product, halide and hydrogenated product of theseepoxy resins, and the like. Any one kind of these epoxy resins may beused alone or two or more kinds thereof may be mixed.

As the epoxy resin, bisphenol A type epoxy resin, naphthol type epoxyresin, naphthalene type epoxy resin, biphenyl type epoxy resin and epoxyresin having butadiene structure are preferable, from the aspects ofheat resistance, insulation reliability and close adhesion to metalfilms. Specifically, for example, liquid bisphenol A type epoxy resin(“Epikote 828EL” manufactured by Japan Epoxy Resins Co., Ltd.),naphthalene type bifunctional epoxy resin (“HP4032”, “HP4032D”manufactured by DIC Corporation), naphthalene type tetrafunctional epoxyresin (“HP4700” manufactured by DIC Corporation), naphthol type epoxyresin (“ESN-475V” manufactured by Tohto Kasei Co., Ltd.), epoxy resinhaving a butadiene structure (“PB-3600” manufactured by DAICEL CHEMICALINDUSTRIES, LTD.), epoxy resin having a biphenyl structure (“NC3000H”,“NC3000L” manufactured by Nippon Kayaku Co., Ltd., “YX4000” manufacturedby Japan Epoxy Resins Co., Ltd.) and the like can be mentioned.

A thermoplastic resin is added for the purpose of imparting suitableflexibility to a composition after curing and the like and, for example,phenoxy resin, polyvinyl acetal resin, polyimide, polyamideimide,polyethersulfone, polysulfone and the like can be mentioned. Any onekind of these thermoplastic resins may be used alone or two or morekinds thereof may be mixed. The thermoplastic resin is preferably addedin a proportion of 0.5 to 60 mass %, more preferably 3 to 50 mass %,relative to a nonvolatile component in the thermosetting resincomposition as 100 mass %.

Specific examples of the phenoxy resin include FX280, FX293 manufacturedby Tohto Kasei Co., Ltd., YX8100, YL6954, YL6974 manufactured by JapanEpoxy Resins Co., Ltd. and the like.

The polyvinyl acetal resin is preferably polyvinyl butyral resin.Specific examples of the polyvinyl acetal resin include Denka Butyral4000-2, 5000-A, 6000-C, 6000-EP manufactured by DENKI KAGAKU KOGYOKABUSHIKI KAISHA, S-LEC BH series, BX series, KS series, BL series, BMseries manufactured by SEKISUI CHEMICAL CO., LTD. and the like.

Specific examples of the polyimide include polyimide “RIKACOAT SN20” and“RIKACOAT PN20” manufactured by New Japan Chemical Co., Ltd. Moreover,linear polyimide obtained by reacting a bifunctional hydroxylgroup-terminated polybutadiene, a diisocyanate compound and tetrabasicacid anhydride (one described in JP-A-2006-37083), modified polyimidesuch as polyimide having a polysiloxane skeleton (those described inJP-A-2002-12667, JP-A-2000-319386 etc.) and the like can be mentioned.

Specific examples of the polyamideimide include polyamideimide “VYLOMAXHR11NN”, and “VYLOMAX HR16NN” manufactured by Toyobo Co., Ltd. Inaddition, examples thereof include modified polyamideimide such aspolysiloxane skeleton-containing polyamideimides “KS9100” and “KS9300”manufactured by Hitachi Chemical Co., Ltd and the like.

Specific examples of the polyethersulfone include polyethersulfone“PES5003P” manufactured by Sumitomo Chemical Co., Ltd. and the like.

Specific examples of the polysulfone include polysulfone “P1700”,“P3500” manufactured by Solvay Advanced Polymers K.K and the like.

Examples of the curing agent include amine series curing agents,guanidine series curing agents, imidazole series curing agents, phenolseries curing agents, naphthol series curing agents, acid anhydrideseries curing agents, epoxy adducts thereof, microencapsulated productsthereof, cyanate ester resins and the like. Of these, phenol seriescuring agents, naphthol series curing agents and cyanate ester resinsare preferable. In the present invention, the curing agent may be usedalone or in a combination of two or more kinds.

Specific examples of the phenol series curing agents and naphthol seriescuring agents include MEH-7700, MEH-7810, MEH-7851 (manufactured byMeiwa Plastic Industries, Ltd), NHN, CBN, GPH (manufactured by NipponKayaku Co., Ltd.), SN170, SN180, SN190, SN475, SN485, SN495, SN375,SN395 (manufactured by Tohto Kasei Co., Ltd.), LA7052, LA7054, LA3018,LA1356 (manufactured by DIC Corporation) and the like.

In addition, specific examples of the cyanate ester resin includebifunctional cyanate resins such as bisphenol A dicyanate, polyphenolcyanate(oligo(3-methylene-1,5-phenylene cyanate),4,4′-methylenebis(2,6-dimethylphenyl cyanate), 4,4′-ethylidenediphenyldicyanate, hexafluorobisphenol A dicyanate,2,2-bis(4-cyanate)phenylpropane, 1,1-bis(4-cyanatephenylmethane),bis(4-cyanate-3,5-dimethylphenyl)methane,1,3-bis(4-cyanatephenyl-1-(methylethylidene))benzene,bis(4-cyanatephenyl)thioether, bis(4-cyanatephenyl)ether and the like,multifunctional cyanate resins derivatized from phenol novolac, cresolnovolac and the like, prepolymers wherein these cyanate resins arepartly converted into triazine and the like. Examples of thecommercially available cyanate ester resin include phenol novolac typemultifunctional cyanate ester resin (“PT30” manufactured by Lonza JapanLtd., cyanate equivalent 124), prepolymer wherein bisphenol A dicyanateis partly or entirely triazined into a trimer (“BA230” manufactured byLonza Japan Ltd., cyanate equivalent 232) and the like.

The mixing ratio of the thermosetting resin and the curing agent isappropriately determined according to the kinds of the thermosettingresin and the curing agent and the like. When the thermosetting resin isan epoxy resin, for example, the mixing ratio of the epoxy resin and thecuring agent in the case of phenol series curing agent or naphtholseries curing agent is preferably a ratio of phenolic hydroxyl groupequivalent of the curing agent of within the range of 0.4 to 2.0, morepreferably within the range of 0.5 to 1.0, relative to 1 epoxyequivalent of the epoxy resin. In the case of a cyanate ester resin, theratio of a cyanate equivalent is preferably within the range of 0.3 to3.3, more preferably 0.5 to 2, relative to 1 epoxy equivalent, ispreferable.

The thermosetting resin composition can further contain, in addition toa curing agent, a curing accelerator. Examples of such curingaccelerators include imidazole series compounds, organic phosphineseries compounds and the like, and specific examples include2-methylimidazole, triphenylphosphine, and the like. When a curingaccelerator is used, it is preferably used in a proportion of 0.1 to 3.0mass % relative to the epoxy resin. When a cyanate ester resin is usedas the epoxy resin curing agent, an organic metal compoundconventionally used as a curing catalyst in a system using an epoxyresin composition and a cyanate compound in combination may be added toshorten the curing time. The organic metal compound includes organiccopper compounds such as copper(II) acetylacetonate and the like,organic zinc compounds such as zinc(II) acetylacetonate and the like,organic cobalt compounds such as cobalt(II) acetylacetonate, cobalt(III)acetylacetonate and the like, and the like. The amount of the organicmetal compound to be added is generally within the range of 10 to 500ppm, preferably 25 to 200 ppm, based on the metal, relative to thecyanate ester resin.

The thermosetting resin composition may contain an inorganic filler forlow thermal expansion of the composition after curing. Examples of theinorganic filler include silica, alumina, isinglass, mica, silicate,barium sulfate, magnesium hydroxide, titanium oxide, and the like.Silica and alumina are preferable, and silica is particularlypreferable. From the aspect of insulation reliability, the inorganicfiller preferably has an average particle size of not more than 3 μm,more preferably not more than 1.5 μm. The content of the inorganicfiller in the thermosetting resin composition is preferably 20 to 60mass %, more preferably 20 to 50 mass %, when the nonvolatile componentof the thermosetting resin composition is 100 mass %.

The thermosetting resin composition can contain other components wherenecessary. Examples of other components include flame retardants such asan organic phosphorus series flame retardant, an organicnitrogen-containing phosphorus compound, a nitrogen compound, a siliconeseries flame retardant, a metal hydroxide, and the like, organic fillerssuch as a silicone powder, a nylon powder, a fluorine powder, and thelike, thickeners such as ORBEN, BENTON, and the like, silicone series,fluorine series, polymer series antifoaming agents and leveling agents,close adhesion imparting agents such as imidazole series, thiazoleseries, triazole series, silane series coupling agents and the like,colorants such as phthalocyanine blue, phthalocyanine green, iodinegreen, disazo yellow, carbon black etc. and the like.

The prepreg can be produced by a known hot-melt method, a solventmethod, and the like. According to the hot-melt method, a prepreg isproduced by once coating, without dissolving a resin composition in anorganic solvent, a resin composition to a releasing paper showing goodrelease property from a resin composition and laminating the same on asheet-like fiber substrate, or directly coating the same with a diecoater and the like. According to the solvent method, a sheet-like fibersubstrate is immersed in a resin composition varnish obtained bydissolving a resin composition in an organic solvent to allow thesheet-like fiber substrate to be impregnated with the resin compositionvarnish, and dried thereafter. It is also possible to prepare a prepregby continuously thermal laminating adhesive films comprised of athermosetting resin composition, which are laminated on a support film,under the conditions of heating and pressing from both surfaces of asheet-like fiber substrate. Examples of the organic solvent used forpreparing varnish include ketones such as acetone, methylethyl ketone,cyclohexanone, and the like, acetic acid esters such as ethyl acetate,butyl acetate, cellosolve acetate, propylene glycol monomethyletheracetate, carbitol acetate, and the like, carbitols such as cellosolve,butyl carbitol, and the like, aromatic hydrocarbons such as toluene,xylene, and the like, dimethylformamide, dimethylacetamide,N-methylpyrrolidone, and the like. Such organic solvent may be usedalone or in a combination of two or more kinds.

While the drying conditions are not particularly limited, when a prepregis laminated on a circuit board and the like, it is important to preventprogress of curing of a thermosetting resin composition as far aspossible during drying so that the adhesion ability of the prepreg canbe retained. In addition, since a large amount of an organic solventremaining in a prepreg causes development of swelling after curing, theprepreg is dried such that the content ratio of the organic solvent in athermosetting resin composition is generally not more than 5 mass %,preferably not more than 2 mass %. While specific drying conditions varydepending on the curability of a thermosetting resin composition and theamount of an organic solvent in varnish, for example, a varnishcontaining 30 to 60 mass % of an organic solvent can be generally driedat 80 to 180° C. for about 3 to 13 minutes. Those of ordinary skill inthe art can appropriately set preferable drying conditions by a simpleexperiment.

Examples of the preparation method of the adhesive sheet, wherein aprepreg is formed on a support film, of the present invention include amethod comprising conveying a prepreg and a support to a roll typelaminating apparatus, and continuously pressing and heating the supportfilm to the prepreg by a metal roll or elastic material roll to give alaminate. In addition, when an adhesive sheet having a protection filmis prepared, a method comprising conveying a prepreg, a support and aprotection film to a roll type laminating apparatus such that thesupport film contacts one surface of the prepreg and the protection filmcontacts another surface, and pressing and heating with a metal roll oran elastic material roll from the surfaces of both the support film andthe protection film to give a laminate can be mentioned. A roll-likeadhesive sheet is prepared by winding the obtained adhesive sheet afterthe lamination. In addition, these adhesive sheets can be efficientlyproduced by continuous preparation after the production step of aprepreg. For example, a sheet-like fiber substrate wound in a roll iscontinuously conveyed by being rolled, immersed in a varnish of athermosetting resin composition and dried, and can be directly subjectedto a preparation step of an adhesive sheet.

As the support film, a plastic film is preferably used. Examples of theplastic film include polyesters such as poly(ethylene terephthalate)(hereinafter to be sometimes abbreviated as “PET”), poly(ethylenenaphthalate) (hereinafter to be sometimes abbreviated as “PEN”), and thelike, polycarbonate (hereinafter to be sometimes abbreviated as “PC”),acrylic (PMMA), cyclic polyolefin, triacetyl cellulose (TAC), polyethersulfide (PES), polyether ketone, polyimide, and the like. Among these, apoly(ethylene terephthalate) film and a poly(ethylene naphthalate) filmare preferable, and a low-cost poly(ethylene terephthalate) film isparticularly preferable. The support film may be subjected to a mattreatment or a corona treatment of the surface on the prepreg side. Toafford a support film which is detachable after thermal curing of aprepreg, as the support film, a support film with a release layerwherein the release layer is present on the side where the support filmand the prepreg are contacted is preferably used.

When a support film with a release layer is used, the support film iseasily detached (delamination) from a prepreg in an auto cutter duringthe process of conveying the adhesive sheet. When the detachment isdeveloped, inconveniences occur since wrinkles are developed in thesupport film in a later lamination step, the prepreg contains a void andthe like. To suppress such detachment, it is important that a supportfilm should be detacheable after thermal curing of a prepreg, and thepeel strength of the support film from the prepreg before thermal curingshould be not less than 1.5 gf/50 mm in 180-degree peel strength. Suchpeel strength (180-degree peel strength) is more preferably not lessthan 1.6 gf/50 mm, further preferably not less than 1.7 gf/50 mm. Theupper limit of such peel strength is not particularly set as long as asupport film in the adhesive sheet is detachable after thermal curing ofa prepreg. It is generally considered to fall within the range of notmore than 5 gf/50 mm.

A release agent to be used for the release layer of a support film witha release layer is not particularly limited as long as the support filmis detachable after thermal curing of the prepreg and the 180-degreepeel strength of the support film before thermal curing of the prepregis not less than 1.5 gf/50 mm. Preferable examples thereof include analkyd resin series release agent and the like. The silicone, seriesrelease agent widely used for the release layer is generally superior inthe release property. When a release layer containing the same as a maincomponent is used, it is difficult to achieve a peel strength of thesupport film before thermal curing of a prepreg of not less than 1.5gf/50 mm in 180-degree peel strength. However, since release property ofthe silicone series release agent can be controlled by adding acellulose derivative such as methylcellulose, ethylcellulose,acetylcellulose and the like, an alkyd resin and the like, a releaselayer having a 180-degree peel strength of the support film beforethermal curing of a prepreg of not less than 1.5 gf/50 mm may beprepared by controlling such release property.

The thickness of the release layer of the support film with the releaselayer is generally about 0.01 to 1 μm, preferably 0.01 to 0.2 μm.

In the present invention, moreover, the support film with a releaselayer may be a commercially available product. For example, a PET filmhaving a release layer containing an alkyd resin series release agent asa main component, such as SK-1, AL-5 and AL-7 manufactured by LintecCorporation, and the like, can be mentioned.

The above-mentioned peel strength (i.e., peel strength between thesupport film and prepreg before thermal curing of prepreg) tends toincrease as the thickness of the support film grows. However, when thethickness of the support film is too large, continuous production tendsto be difficult since conveying of the film by vacuum adsorption in anauto cutter becomes difficult, and the like. When the thickness of thesupport film is too small, the peel strength tends to be too small, andcontinuous production tends to be difficult since a phenomenon ofwinding of a temporarily fit adhesive sheet in a roll (curling) occursand the like. In the present invention, therefore, the thickness of thesupport film is preferably within the range of 20 to 50 μm, morepreferably within the range of 20 to 45 μm, particularly preferablywithin the range of 23 to 40 μm. The thickness of the support film inthe present invention includes that of a release layer when a supporthas the release layer.

The peel strength (180-degree peel strength) between a support film anda prepreg before thermal curing of the prepreg can be measured accordingto the following method. An adhesive sheet is cut in a 50 mm width. Whena protection film is present, the film is detached. Then, the prepregside is adhered to a reinforced plate with a double-faced adhesive tape,and the peel strength on peeling the support film in the 180-degreedirection is measured by a tensile tester. Examples of the tensiletester include Autograph AGS-J series manufactured by SHIMADZUCORPORATION and the like. As the peeling rate, for example, 200 mm/minis adopted.

In the present invention, the thickness of the prepreg is preferably 20to 100 μm. When the thickness of the prepreg is less than 20 μm, aprepreg tends to be not laminated flatly on a circuit board. When thethickness exceeds 100 μm, a thin multi-layer printed wiring board cannotbe obtained conveniently, and conveying of a film by vacuum adsorptionin an auto cutter tends to be difficult.

The adhesive sheet in the present invention preferably has a protectionfilm. In other words, the adhesive sheet is preferably has a layerconstitution of protection film/prepreg/support film. The protectionfilm provides advantages such as protection of the prepreg surface froma physical damage when setting a prepreg with a support film in an autocutter, prevention of attachment of foreign substance (dirt etc.) andthe like. Examples of the protection film include polyolefin such aspolyethylene, polypropylene, polyvinyl chloride, and the like, polyestersuch as PET, PEN, and the like, polycarbonate (PC), polyimide, and thelike. Like a support film, a protection film may also be subjected to amat treatment, a corona treatment as well as a release treatment. Thethickness of the protection film is preferably within the range of 5 to30 μm. When it is less than 5 μm, since the protection film is thin andeasily extended, close adhesion to the prepreg surface tends to bedifficult during production. When it exceeds 30 μm, the film isunpreferably disadvantageous in cost.

The temporary fitting preparatory step and the temporary fitting step inthe present invention are explained as follows. In the temporary fittingpreparatory step, a roll-like adhesive sheet slit in the width of acircuit board is first set in an auto cutter. For lamination on bothsurfaces of a circuit, two roll-like adhesive sheets are set on theupper and lower sides, and for lamination on one surface alone, oneadhesive sheet is set. When the adhesive sheet has a protection film,the protection film is detached from a prepreg surface while taking upthe film by a take-up roll. The adhesive sheet can be mechanicallyconveyed after fixing the adhesive sheet by vacuum adsorption from thesupport film side. The adhesive sheet is conveyed and configured suchthat the support film comes outside, namely, the prepreg surface comesinto contact with one or both of the surfaces of the circuit board. Inthe temporary fitting step, for example, an adhesive sheet is partlyadhered to a circuit board at an unnecessary part, which is a part ofthe front portion in the feeding direction of the substrate and notsuperimposed on a circuit in need of lamination, by heating and pressingthe part of the adhesive sheet from the support film side. While theadhesion conditions vary depending on the thermosetting resincomposition used for a prepreg and melt viscosity thereof, it isgenerally compression bonded at a temperature of 60 to 130° C. for about1 to 10 sec. Thereafter, the adhesive sheet is conveyed with the circuitboard, and cut according to the size of the substrate with a cutter,whereby the adhesive sheet is temporarily fit to the circuit board.During cutting, a cutter backup heater heated to 40 to 80° C. ispreferably set to reduce generation of cutting scrap of the resincomposition (resin chip).

The temporary fitting preparatory step and the temporary fitting step inthe present invention can be successively performed using a commerciallyavailable auto cutter. Examples of the commercially available autocutter include a dry film laminating machine Mach series manufactured byHakuto Co., Ltd., auto cutters FAC-500 and SAC-500/600 manufactured byShin-Ei Kiko Co., Ltd., and the like.

Then, a laminating step is explained. An adhesive sheet temporarily fitto a circuit board is heated and pressed under reduced pressure tolaminate the adhesive sheet on the circuit board. The heating andpressing in the laminating step can be performed by pressing a heatedmetal plate such as SUS mirror plate and the like from the support filmside. However, the metal plate is preferably pressed via an elasticmaterial such as heat resistant rubber and the like, rather than directpressing, so that the adhesive sheet will sufficiently follow circuitconcaves and convexes of the circuit board. The pressing is performed ina temperature range of preferably 70 to 140° C. and pressure range ofpreferably 1 to 11 kgf/cm² (9.8×10⁴ to 107.9×10⁴ N/m²). The air pressureis preferably a reduced pressure of preferably not more than 20 mmHg(26.7 hPa). After the laminating step, the laminated adhesive sheet issmoothed preferably by a hot press with a metal plate. The smoothingstep is performed by heating and pressing the adhesive sheet with aheated metal plate such as SUS mirror plate and the like under normalpressure (atmospheric pressure). The heating and pressing conditions aresimilar to those in the above-mentioned laminating step.

The laminating step and smoothing step in the present invention can besuccessively performed using a commercially available vacuum laminatingmachine. Examples of the commercially available vacuum laminatingmachine include vacuum pressing type laminating machine manufactured byMEIKI Co., Ltd., vacuum applicator manufactured by Nichigo-Morton Co.,Ltd. and the like.

After the laminating step or after the smoothing step, a thermal curingstep is performed. In the thermal curing step, a prepreg is thermallycured to form an insulating layer.

While the thermal curing conditions vary depending on the kind and thelike of the thermosetting resin composition, the curing temperature isgenerally about 170 to 190° C., and curing time is about 15 to 60minutes.

The production method of the multi-layer printed wiring board of thepresent invention further includes a step of detaching a support filmfrom a thermally cured prepreg (insulating layer). The support film maybe manually detached or mechanically detached by an automatic detachingapparatus.

The production method of the multi-layer printed wiring board of thepresent invention may further contain a drilling step for drilling aninsulating layer, a roughening step for roughening an insulating layer,a plating step for forming a conductive layer on a roughened insulatinglayer surface by plating, and a circuit forming step for forming acircuit on a conductive layer. These steps can be performed according tovarious methods known to those of ordinary skill in the art and used forthe production of multilayer printed wiring boards.

The drilling step can be performed, for example, by forming a hole suchas via hole (blindvia), through-hole and the like in an insulating layerwith a drill, laser such as carbon dioxide gas laser, YAG laser and thelike, plasma and the like. The blindvia in a high density wiring ispreferably formed by a laser. While UV-YAG laser shows fineprocessability on glass cloth, it is not necessarily satisfactory fromthe aspects of cost and processing speed. On the other hand, carbondioxide gas laser is superior to UV-YAG laser in processing speed andcost; however, processability is not fine. For example, when blindviaand the like are formed by applying carbon dioxide gas laser to aprepreg, glass cloth protrudes from the blindvia side wall due todifferent processability between the glass cloth and the thermosettingresin, and the concave and convex of the wall surface increase. Suchconcave and convex of the side surface of a blindvia decreasesconduction reliability, and causes a remarkable problem particularly ina high density printed wiring board having a pore size of not more than100 μm. When the energy of carbon dioxide gas laser is increased toenhance processability of glass cloth, the insulating layer surfacereceives a greater damage, the size of the surface of the pore (diameterof via top) is processed to become large, and the concave and convex ofthe insulating layer surface near the pore increase, which isinconvenient for forming an ultrafine wiring. In contrast, when ablindvia (via hole) is formed by laminating an adhesive sheet, wherein aprepreg is formed on a support film, on a circuit board, thermal curingthe prepreg without detaching the support film to form an insulatinglayer, and applying carbon dioxide gas laser of the support film, thedamage on the insulating layer surface is suppressed, and the glasscloth is processed successfully even when carbon dioxide gas laser withhigh energy is applied. Therefore, a blindvia is preferably formedbetween the thermal curing step and the detaching step, and a blindviais preferably formed by applying carbon dioxide gas laser on a supportfilm after forming an insulating layer by thermally curing a prepreg. Inaddition, as a support film, a plastic film is preferable as mentionedabove, and a poly(ethylene terephthalate) film is particularlypreferable. When an insulating layer is formed using an adhesive layerfree of a fiber substrate, such problem does not occur since it can beprocessed with a lower energy.

The carbon dioxide gas laser used generally has a wavelength of 9.3 to10.6 μm. The energy of the carbon dioxide gas laser is preferably notless than 1 mJ. When the energy is too low, a fiber substrate protrudesfrom the pore side wall due to low processability of the fibersubstrate, and the concave and convex of the wall surface tend toremarkably increase. In addition, increase of processing speed bydecreasing the shot number also becomes difficult. Since a higher upperlimit of the energy causes damage on underlying conductive layer of theblindvia, the upper limit is inevitably determined. Depending on theshot number, depth of blindvia and the like, it is generally not morethan 5 mJ, preferably not more than 4.5 mJ, more preferably not morethan 4 mJ, particularly preferably not more than 3.5 mJ.

While the shot number also varies depending on the depth of blindvia andpore size, it is generally 1 to 10 shots. To increase processing speed,a smaller shot number is preferable. Using a high energy value, ablindvia can be processed by 1 or 2 shots, and the productivity of amulti-layer printed wiring board can be strikingly improved. Thus, theenergy of the carbon dioxide gas laser is more preferably not less than1.5 mJ, further preferably not less than 2 mJ, from the aspect ofprocessing speed. For processing with plural shots, since a burst modeemploying continuous shots accumulates processing heat in the pore, adifference in the processability easily occurs between a fiber substrateand a thermosetting resin composition and concave and convex of the poreside wall tend to be large. Thus, a cycle mode employing plural shotswith time intervals is preferable.

The pulse width of the carbon dioxide gas laser is not particularlylimited, and can be selected from a wide range of from a middle range of28 μs to a short pulse of about 4 μs.

The energy of carbon dioxide gas laser is an energy value of laser on aninsulating layer surface per one shot, which can be adjusted based onthe output of oscillator, collimation lens (lens for energy control),mask diameter and the like of a carbon dioxide gas laser apparatus. Themask diameter is selected according to the diameter of a blindvia to beprocessed. The energy value can be measured by placing a measurementdevice (power sensor) on a table on which laser processing is performedand measuring the energy at the height of the insulating layer surfaceof a circuit board to be processed. Commercially available carbondioxide gas laser apparatuses are equipped with a measurement apparatus,and the energy on an irradiation target surface can be easily measured.Examples of the commercially available carbon dioxide gas laserapparatus include ML605GTWII manufactured by Mitsubishi ElectricCorporation, LC-G series manufactured by Hitachi Via Mechanics, Ltd.,substrate drilling laser processing machine manufactured by MatsushitaWelding Systems Co., Ltd. and the like.

Where necessary, a through-hole may be formed in a circuit board havingan insulating layer. A through-hole can be formed according to aconventionally-known method. In a multi-layer printed wiring board, athrough-hole is generally formed in a core substrate, and a build-upinsulating layer is generally conducted by a blindvia. In addition, adrilling machine is generally used for forming a through-hole. A methodof forming a through-hole in a core substrate by laser is known. In thiscase, since a copper foil reflects laser, a method including chemicallyprocessing a copper foil surface and applying laser is generallyemployed. In addition, a method including setting a drilling aid sheetcontaining a component improving laser energy absorption on a copperfoil surface and applying laser is also known. When a through-hole isformed by carbon dioxide gas laser, a greater energy is necessary and,for example, 10 to 60 mJ of energy is employed, though subject to changedepending on the thickness of the copper foil and core substrate. In athin circuit board, for example, like formation of a blindvia in thepresent invention, a through-hole may be formed by applying a laser on abuilt-up insulating layer, such as formation of a through-hole byapplying a carbon dioxide gas laser on a support film closely adhered tothe insulating layer surface and the like.

The production method of the multi-layer printed wiring board of thepresent invention further contains a detaching step including detachinga support film from a thermally cured prepreg (insulating layer). Asupport film may be detached manually or mechanically detached by anautomatic detaching apparatus. A support film is preferably detachedafter formation of a blindvia. When a through-hole is formed, it ispreferably formed after formation of a blindvia, or after formation of ablindvia and a through-hole.

A roughening step can be performed, for example, by treating aninsulating layer surface with an oxidant such as an aqueous alkalinepermanganate solution and the like. The roughening step sometimes actsas a desmear step of a hole such as via hole, through hole and the like.Prior to treatment with an aqueous alkaline permanganate solution, aswelling treatment with a swelling solution is preferably performed.Examples of the swelling solution include Swelling Dip Securiganth P andSwelling Dip Securiganth SBU manufactured by Atotech Japan K. K. and thelike. The swelling treatment is generally performed by immersing aninsulating layer in a swelling solution heated to about 60 to 80° C. forabout 5 to 10 minutes. Examples of the aqueous alkaline permanganatesolution include a solution obtained by dissolving potassiumpermanganate or sodium permanganate in an aqueous solution of sodiumhydroxide. A roughening treatment with an aqueous alkaline permanganatesolution is generally performed at 60 to 80° C. for 10 to 30 minutes. Ascommercially available products of the aqueous alkaline permanganatesolution, Concentrate Compact CP and Dosing Solution Securiganth Pmanufactured by Atotech Japan K. K. and the like can be mentioned. Inaddition, after a treatment with an oxidant (aqueous alkalinepermanganate solution), a neutralization treatment with a reducing agentis preferably performed. Examples of the reducing agent (neutralizationsolution) include Reduction Solution Securiganth P manufactured byAtotech Japan K. K. The neutralization treatment is generally performedby immersing an insulating layer in a neutralization solution heated toabout 25 to 60° C. for about 2 to 7 minutes.

A plating step is performed, for example, by forming a conductive layeron the surface of an insulating layer, which has convex and concaveanchors formed by a roughening treatment, by a method combiningelectroless plating and electroplating. As the conductive layer, acopper plating layer is preferable. A copper plating layer is formed bya method combining electroless copper plating and copper electroplating,or a conductive layer is formed by forming a plating resist having apattern reverse to the conductive layer and applying electroless copperplating alone. The thickness of the electroless plating layer ispreferably 0.1 to 3 μm, more preferably 0.3 to 2 μm. As the thickness ofthe electroplating layer, the total thickness with the thickness of theelectroless plating layer is preferably 3 to 35 μm, more preferably 5 to20 μm. After formation of the conductive layer, an annealing treatmentis performed at 150 to 200° C. for 20 to 90 minutes to further improvethe peel strength of the conductive layer and stabilize the conductivelayer.

For a circuit formation step, for example, subtractive process,semi-additive process and the like can be used. For fine line formation,a semi-additive process is preferable, wherein a pattern resist isapplied onto an electroless plating layer, an electrolytic plating layer(pattern plating layer) having a desired thickness is formed, thepattern resist is detached and an electroless plating layer is removedby flash etching to give a circuit.

The circuit substrate to be used for the production of the multilayerprinted wiring board of the present invention mainly refers to a glassepoxy substrate, a metal substrate, a polyester substrate, a polyimidesubstrate, a BT resin substrate, a thermosetting polyphenylene ethersubstrate, and the like, wherein one or both of the surfaces thereofhave a pattern processed conductive layer (circuit). The circuitsubstrate in the present invention also encompasses an internal-layercircuit substrate of an intermediate product, on which an insulatinglayer and/or a conductive layer will be formed for the production of amultilayer printed wiring board. The surface of a conductive circuitlayer is preferably roughened in advance by a blackening treatment andthe like, since close adhesion of an insulating layer to a circuitsubstrate can be achieved.

Other features of the invention will become apparent in the course ofthe following descriptions of exemplary embodiments which are given forillustration of the invention and are not intended to be limitingthereof.

EXAMPLES

In the following Examples and Comparative Examples, “part” means “partsby mass”.

Example 1

Liquid bisphenol A type epoxy resin (epoxy equivalents 180, “Epikote828EL” manufactured by Japan Epoxy Resins Co., Ltd., 28 parts) andnaphthalene type tetrafunctional epoxy resin (epoxy equivalents 163,“HP4700” manufactured by DIC Corporation, 28 parts) were dissolved in amixed solution of methylethyl ketone (15 parts) and cyclohexanone (15parts) with stirring while heating. Thereto were added a methylethylketone solution (110 parts) of a naphthol series curing agent (“SN-485”manufactured by Tohto Kasei Co., Ltd., phenolic hydroxyl groupequivalents 215) having a solid content of 50%, a curing catalyst(“2E4MZ” manufactured by SHIKOKU CHEMICALS CORPORATION, 0.1 part),spherical silica (average particle size 0.5 μm, “SO—C2” manufactured byAdmatechs Company Limited, 70 parts), and a polyvinyl butyral resinsolution (“KS-1” manufactured by SEKISUI CHEMICAL CO., LTD., 30 parts,solid content 15%, 1:1 solution of ethanol:toluene), and the mixture wasuniformly dispersed in a high-speed rotation mixer to give athermosetting resin composition varnish.

A 19 μm-thick glass cloth (1027MS manufactured by Asahi-Schwebel Co.,Ltd.) was impregnated with the varnish and dried at 80 to 120° C. for 6minutes to give a 50 μm-thick prepreg (residual solvent amount was 1 wt% in the thermosetting resin composition without glass cloth). PET with25 μm-thick release layer (AL5: alkyd resin series release agentmanufactured by Lintec Corporation) described in Table 1 was thermallylaminated on one side of a prepreg, and a 16 μm-thick polypropyleneprotection film was thermally laminated on the other side thereof andthe laminate was wound in a roll. Thereafter, the roll was slit at width335 mm to give two 50 m-long adhesive sheet rolls. Then, the rolls wereset in an auto cutter FAC-500 manufactured by Shin-Ei Kiko Co., Ltd. anda temporary fitting test onto a 0.2 mm-thick copper-plated laminateplate with a circuit formed thereon (circuit conductor thickness 18 μm)was performed. The temporary fitting was performed at 100° C. for 3seconds.

The sheet temporarily fit well was laminated on both surfaces of alaminate plate by a vacuum laminating machine manufactured by MEIKI Co.,Ltd. under conditions of temperature 120° C., pressure 7 kgf/cm²,pressure 5 mmHg or below and continuously subjected to a hot press withan SUS mirror panel under conditions of temperature 120° C., pressure 5kgf/cm², atmospheric pressure. Then, the laminate with a PET film wasthermally cured at 180° C. for 30 minutes to form an insulating layer onboth surfaces of the substrate. Thereafter, the release property of thePET film was evaluated by manually detaching the film.

Measurement of detaching strength of support film and prepreg (beforethermal curing).

The detaching strength between a support film and a prepreg was measuredby cutting an adhesive sheet in a width of 50 mm, detaching a protectionfilm, adhering the prepreg side to a reinforced plate with adouble-faced adhesive tape, and measuring the peel strength on peelingthe support film in a 180-degree direction by a tensile tester. Thevalues in the Table are averages of 3 measurements. As the tensiletester, an Autograph AGS-500 manufactured by SHIMADZU CORPORATION wasused, and the peeling speed was 200 mm/minute.

Example 2

By an operation in the same manner as in Example 1 except that PET witha 38 μm-thick release layer (AL5 manufactured by Lintec Corporation:alkyd resin series release agent) described in Table 1 was used,evaluation was performed in the same manner as in Example 1.

Comparative Example 1

By an operation in the same manner as in Example 1 except that PET witha 16 μm-thick release layer (A15 manufactured by Lintec Corporation:alkyd resin series release agent) described in Table 1 was used,evaluation was performed in the same manner as in Example 1.

TABLE 1 Comparative Example 1 Example 1 Example 2 thickness (μm) of 1625 38 support film thickness (μm) of 50 50 50 prepreg detaching strength0.9 1.7 2.3 (gf/50 mm) between support film and prepreg detachment x ∘ ∘(delamination) between support film and prepreg curling of prepreg x ∘ ∘after temporary fitting film delivery in auto ∘ ∘ ∘ cutter detachment ofsupport — ∘ ∘ film after thermal curing

In Table 1, the detaching strength (gf/50 mm) between a support film anda prepreg is that before thermal curing of the prepreg.

In Table 1, the detachment (delamination) between a support film and aprepreg was evaluated by visually observing whether the supporting filmwas detached in 1 cm of both ends of the long side of the adhesive sheetwhen the adhesive sheet wound in a roll was drawn out by about 1 m. Anadhesive sheet free of detachment and delamination between a supportfilm and a prepreg in all regions passed (∘), and an adhesive sheet withdetachment or delamination failed (×).

In addition, curling of a prepreg after temporary fitting was evaluatedby drawing out an adhesive sheet wound in a roll, cutting the sheet in a50 cm length, placing the sheet on a flat table with the supporting filmfacing upward, fixing the side of one tip onto the table, and measuringthe length of the other side shortened by curling. When the shortenedlength (roll back amount) was 5 cm or blow, the adhesive sheet passed(∘), and when it exceeds 5 cm, the adhesive sheet failed (×).

The film delivery in an auto cutter was evaluated by setting an adhesivesheet wound in a roll in “SAC-500 (auto cutter manufactured by Shin-EiKiko Co., Ltd.)”, and visually observing whether the detachment(delamination) occurs on the entire surface between a support film and aprepreg in SAC-500 during the step of conveying the adhesive sheetdelivered from the roll to the temporary fitting step via the autocutter. An adhesive sheet free of detachment (no delamination) on theentire surface passed (∘), and an adhesive sheet with detachment (withdelamination) failed (×).

In addition, detachment of the support film after thermal curing wasevaluated by passing a substrate with an adhesive sheet temporarily fitthereto through a vacuum laminating machine manufactured by MEIKI Co.,Ltd. to laminate the adhesive sheet on the substrate, heating thesubstrate by “SPHH-101 (gear oven manufactured by ESPEC)” at 180° C. for30 minutes to cure the adhesive sheet, and visually observing the stateof the support film after curing. An adhesive sheet having the supportfilm adhered to the prepreg surface after curing passed (∘), and anadhesive sheet with detachment of the support film from the prepregsurface failed (×). The evaluation (−) of detachment of the support filmafter thermal curing in Comparative Example 1 means that thedelamination was developed before curing and evaluation of thedetachment of the support film after thermal curing was not possible.

Example 3 Production of Multi-Layer Printed Wiring Board

The substrate temporarily fit with a prepreg with a support filmobtained in Example 2 was laminated on both surfaces by a vacuumlaminating machine manufactured by MEIKI Co., Ltd. under the conditionsof temperature 120° C., pressure 7 kgf/cm², pressure 5 mmHg or below,and continuously subjected to a hot press with an SUS mirror panel underconditions of temperature 120° C., pressure 5 kgf/cm². Then, thelaminate with a release PET film was heated at 180° C. for 30 minutes tothermally cure the prepreg to form an insulating layer on both surfacesof the substrate. Thereafter, the release PET film was detached, and viahole was formed by laser drilling. For a surface treatment process ofthe insulating layer also serving as a desmear process, the followingchemical solutions manufactured by Atotech Japan K.K. were used.

oxidant “Concentrate Compact CP” (alkaline permanganate solution)

reducing agent “Reduction solution Securiganth P-500”

The insulating layer was subjected to a surface treatment with anoxidant solution at 80° C. for 10 minutes. Then, the layer was subjectedto a neutralization treatment with a reducing agent solution at 40° C.for 5 minutes. A catalyst for electroless copper plating was applied tothe surface of the insulating layer, electroless plating andelectroplating were performed, and the outermost copper layer was etchedto form a circuit to give a 4 layer printed wiring board. Then, anannealing treatment was further conducted at 180° C. for 30 minutes. Theconductive plating of the obtained conductive layer had a thickness ofabout 30 μm, and the peeling strength was 0.8 kgf/cm. The peelingstrength was evaluated according to the Japanese Industrial Standards(JIS) C6481. The obtained multilayer printed wiring board was not warpedby baking at 255° C.×15 minutes.

Comparative Example 2

After laminating and hot pressing in the same manner as in Example 3,the release PET film was detached, and the resulting laminate was heatedat 180° C. for 30 minutes to thermally cure the prepreg therein. Sinceconcaves and convexes (about 3 μm) were developed, along the seam of theglass cloth, on the surface of the resin after thermal curing, theproduct was not usable for the subsequent evaluation. The resin surfacein Example 3 was flat like a support film, and the concaves and convexeson a circuit were about 1 μm and fine. As for the surface flatcharacteristics, a non-contact type surface roughness meter (WYKO NT3300manufactured by Veeco Instruments Inc.) was used (VSI contact mode, 10×lens, measurement range 1.2 mm square), and the concaves and convexeswere evaluated by Rt value (Peak-to-valley) of the surface of theinsulating layer.

Example 4

A 16 μm-thick glass cloth (1027NS manufactured by Arisawa Mfg. Co.,Ltd.) was impregnated with the resin varnish obtained in Example 1 anddried at 80 to 120° C. for 6 minutes to give a 50 μm-thick prepreg(residual solvent amount was 1 wt % in the thermosetting resincomposition without glass cloth). A 38 μm-thick release PET film (AL5:alkyd resin series release agent manufactured by Lintec Corporation) wasthermally laminated from one side of the prepreg and a 16 μm-thickpolypropylene protection film was thermally laminated from the otherside thereof and the laminate was wound in a roll. Thereafter, the rollwas slit at width 335 mm to give a prepreg with a roll-like plasticfilm. Then, the prepreg with the plastic film was cut in 500 mm length,temporarily fit to both surfaces of a copper-plated laminate plate (510mm×340 mm size, thickness 0.2 mm) with a circuit formed thereon (circuitconductor thickness 18 μm), laminated on both surfaces by a vacuumlaminating machine manufactured by MEIKI Co., Ltd. under conditions oftemperature 120° C., pressure 7 kgf/cm², pressure 5 mmHg or below, andcontinuously subjected to a hot m press with an SUS mirror panel underconditions of temperature 120° C., pressure 5 kgf/cm². Then, thelaminate with a release PET film was thermally cured at 180° C. for 30minutes to form an insulating layer on both surfaces of the substrate.

After cooling to room temperature, plural blindvias (assuming topdiameter of 70 μm) were formed by applying a carbon dioxide gas laser(ML605GTWII-P) manufactured by Mitsubishi Electric Corporation on therelease PET film (without being detached) under the conditions describedin FIG. 1, row for Example 4. To adjust the assumed top diameter 70 μmto that in the Comparative Examples, the mask diameter was set to 1.1mm, which is somewhat larger than 1.0 mm set when pores are formedwithout a release PET film in the Comparative Examples to be mentionedlater.

Thereafter, blindvia was observed with a scanning electron microscope(SEM) (type “SU-1500” manufactured by Hitachi High-TechnologiesCorporation) and laser processability was evaluated. After a desmearprocess of the insulating layer also serving as a roughening treatmentprocess, the blindvia was also observed with a scanning electronmicroscope (SEM). The roughening treatment process was performed bysubjecting the laminate to a step of swelling 60·C×5 minutes, oxidation80·C×20 minutes and neutralization 40·C×5 minutes using a rougheningsolution manufactured by Atotech (Swelling Dip Securiganth P (swelling),Concentrate Compact P (oxidation), Reduction Solution Securiganth P(neutralization)).

Example 5

By an operation in the same manner as in Example 4 except that pore wasformed under the conditions described in FIG. 1, row for Example 5,evaluation was performed in the same manner as in Example 4.

Example 6

By an operation in the same manner as in Example 4 except that pore wasformed under the conditions described in FIG. 1, row for Example 6,evaluation was performed in the same manner as in Example 4.

Comparative Examples 3 to 5

A circuit board with an insulating layer formed on both surfaces, whichwas prepared as described in Example 4, was cooled to room temperature,a release PET film was detached, and a pore was formed using carbondioxide gas laser (ML605GTWII-P) manufactured by Mitsubishi ElectricCorporation (mask diameter 1.0 mm) under the conditions described inFIG. 2 (Comparative Examples 3 to 5). Other than that, by an operationin the same manner as in Example 4, evaluation was performed in the samemanner as in Example 4.

The results are shown in FIG. 1 and FIG. 2. As SEM photograph, the partwith high glass cloth density is representatively shown.

As is clear from FIG. 1, any blindvia formed by applying carbon dioxidegas laser on the support film was superior in the circularity of via,the resin was damaged less even with high energy exceeding 1 mJ, and theinsulating layer around the via had a uniform rough surface afterdesmearing. Moreover, since high energy is used, via processing ispossible even when the number of shots is reduced, and it is clear thatthe method of the present invention is a pore formation method suitablefor high-speed formation of via.

On the other hand, it is clear from FIG. 2, wherein a blindvia wasformed by directly applying carbon dioxide gas laser to the insulatinglayer after detachment of the support film, that processabilitydecreased and protrusion of glass cloth became noticeable in ComparativeExamples 3 and 4 using low energy. In Comparative Example 5 wherein theenergy was comparatively high and 1 mJ, protrusion of glass cloth wascomparatively suppressed; however, since the circularity of the via waspoor and the resin of the insulating layer surface near the via washighly damaged, the via top diameter expanded remarkably afterdesmearing.

Where a numerical limit or range is stated herein, the endpoints areincluded. Also, all values and subranges within a numerical limit orrange are specifically included as if explicitly written out.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

All patents and other references mentioned above are incorporated infull herein by this reference, the same as if set forth at length.

1. A method of producing a multi-layer printed wiring board, comprising:(a) conveying an adhesive sheet from an adhesive sheet roll, wherein anadhesive sheet having a prepreg formed on a support film is wound in aroll, and placing said adhesive sheet such that a surface of saidprepreg contacts one or both of the surfaces of a circuit board; (b)partially adhering said adhesive sheet to said circuit board by heatingand pressing a part of said adhesive sheet from the support film side,and cutting said adhesive sheet according to the size of said circuitboard with a cutter, to obtain a temporarily fitted adhesive sheet; (c)heating and pressing said temporarily fitted adhesive sheet underreduced pressure to laminate said adhesive sheet on said circuit board;(d) thermally curing said prepreg, to obtain an insulating layer; and(e) detaching said support film after said thermally curing, whichmethod enables continuous production of an insulating layer of amultilayer printed wiring board by performing said (a)-(e).
 2. Themethod according to claim 1, wherein, in said adhesive sheet, saidsupport film has a release layer on the surface side in contact withsaid prepreg, and the peel strength of said support film from saidprepreg before thermal curing is not less than 1.5 gf/50 mm at180-degree peel strength.
 3. The method according to claim 1, wherein,in said adhesive sheet, said support film has a thickness of 20 to 50 μmand said prepreg has a thickness of 20 to 100 μm.
 4. The methodaccording to claim 1, wherein said placing said adhesive sheet such thata surface of said prepreg contacts one or both of the surfaces of acircuit board and said partially adhering said adhesive sheet to saidcircuit board are performed by an auto cutter.
 5. The method accordingto claim 1, wherein said heating and pressing said temporarily fittedadhesive sheet under reduced pressure to laminate said adhesive sheet onsaid circuit board is performed by a vacuum laminating machine.
 6. Themethod according to claim 1, wherein said adhesive sheet has a layerconstitution of protection film/prepreg/support film, and saidprotection film is detached by winding during said conveying of saidadhesive sheet.
 7. The method according to claim 6, wherein, in saidadhesive sheet, said protection film has a thickness of 5 to 30 μm. 8.The method according to claim 1, wherein said heating and pressing areperformed via an elastic material in the laminating step.
 9. The methodaccording to claim 8, further comprising, after said heating andpressing said temporarily fitted adhesive sheet under reduced pressureto laminate said adhesive sheet on said circuit board, heating andpressing said adhesive sheet under normal pressure with a metal plate.10. The method according to claim 1, further comprising drilling saidinsulating layer, roughening said insulating layer, to obtain aroughened insulating layer surface, forming a conductive layer on saidroughened insulating layer surface by plating, and forming a circuit onsaid conductive layer.
 11. The method according to claim 10, whereinsaid drilling is performed between said thermally curing said prepregand said detaching said support film.
 12. The method according to claim10, wherein said drilling comprises forming a via hole by applying acarbon dioxide gas laser on the top of said support film.
 13. The methodaccording to claim 12, wherein said carbon dioxide gas laser has anenergy of not less than 1 mJ.
 14. The method according to claim 12,wherein said energy of said carbon dioxide gas laser is 1 mJ to 5 mJ.15. The method according to claim 1, wherein said support film is apoly(ethylene terephthalate) film.
 16. The method according to claim 1,wherein said prepreg comprises a glass cloth impregnated with athermosetting resin composition.